[GRASSLIST:9580] filtering with FFT

[Martin Landa]

Hi all,

according to OSS GIS: A GRASS GIS Approach (see page 243) I am trying
to apply high pass filter with FFT. I always get a strange result
image (see the attached file).

g.region rast=tm1
i.fft in=tm1 real=tm1_r imag=tm1_i
g.region rast=tm1_r
r.circle -b out=ff coord=-769058,-988168 max=1550
r.mapcalc 'MASK=if(isnull(ff),1,null())'
i.ifft real=tm1_r imag=tm1_i out=tm1_hp
g.remove rast=MASK
g.region rast=tm1
r.colors map=tm1_hp col=grey.eq
d.rast tm1_hp

I don't know where I am wrong ... Does anyone have the same problem?

Thanks for help, best regards,

Martin
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